This invention relates to tractor-trailers and more particularly, to systems that facilitate efficient pneumatic connection between a tractor and a trailer.
Tractor-type trucks are designed to tow trailers and semi-trailers having large loads. The loads may include goods, supplies or other freight. Tractor trucks and trailers rely on air pressure for brake control. Air is supplied by the tractor to the trailer via air hoses. Pneumatic interconnection between the tractor and trailer is made by the well known “glad-hand” devices. A glad hand from the tractor can be coupled to a glad hand from the trailer to provide an air-tight seal.
A truck, made up of a tractor and a trailer for example, has two types of brakes. These are service brakes and parking brakes. Parking brakes may also be referred to as emergency brakes or as spring brakes.
In order to permit vehicle motion, pressurized air is used to compress the emergency brake springs (i.e. to release the emergency brake). In order to stop the vehicle using the emergency brake (i.e. to apply the emergency brake), the springs are released by releasing the pressurized air from the spring brake chambers. The air system is used to engage or disengage the brakes on a truck. Pressurized air (or, high pressure air) in the brake system is supplied by a compressor powered by the engine.
The tractor portion of a truck can be designed to connect with the air lines of the trailer at one of a number of locations (of the tractor). While a tractor is usually designed with one set of glad hands, the tractor can also be designed with two sets of glad hand connections. A tractor with two sets of glad hand connections as illustrated in FIG. 1. Tractor 100 may include glad hands 115 at the backside of a cab portion 110 and glad hands 125 near the rear end of the chassis frame 120. One or the other of these glad hands 115 and 125 (but not both) will be connected to a trailer. Only one glad hand can supply the pressurized air. A trailer (not illustrated) includes at least a set of glad hands that can be connected to one of glad hand 115 and 125. The glad hand that is connected to the trailer provides or supplies pressurized air to the trailer (while the glad hand that is not connected to the trailer cannot supply air). The connection via glad hands 115 can be referred to as the semi position connection while the connection via glad hands 125 can be referred to as the full position connection.
Depending on the type of trailer being attached to the tractor, one of the two sets of glad hands 115 and 125 is utilized to supply air. Currently, switching the air supply between the sets of glad hands involves manual reconfiguration. Multiple valves may have to be turned or plugged and hose connections have to be disconnected and reconnected. Such actions increase the time and labor costs. These actions are also subject to human errors.
Other systems have been proposed that include a selector for switching between the different sets of glad hands. The location of these selectors makes them susceptible to being accidentally switched from one source to another by conditions on the road such as a pebble hitting the selector for example. Such switch in air delivery from one set of glad hands connected to the trailer to another set of glad hands not connected to the trailer while the vehicle is in motion leads to undesirable consequences. In some situations, it is also preferable to place the selector in a secure location.
What is desired, therefore, is a selection mechanism that is secure and is incapable of switching connections while the vehicle is in motion or while the emergency brakes are released.